The use of backscattered electron imaging mode to assess the effect of fine dispersions on development of superplastic microstructures in Al-Mg alloys

Abstract

Microstructural evolution during thermomechanical processing of several Al-Mg alloys was studied using backscattered orientation contrast imaging in the scanning electron microscope. The microstructural evolution in A1-8Mg-0.1Zr was characterized in three phases: (a) in the initial stages, precipitation occurred on prior boundaries and microbands were observed in the grain interiors; (b) during intermediate stages, higher order microbands were observed and precipitates formed throughout the microstructure on both lower- and higher-order microbands; (c) in the final stages, equiaxed regions appeared around larger particles suggesting particle stimulated nucleation of recrystallization. A higher Mg-content alloy (A1-10Mg0.1Zr) was compared at two stages and seen to provide a greater volume fraction of similar sized precipitate. A finer recrystallized microstructure and greater superplastic response was observed in the Al-10Mg-0.1Zr alloy.